During the next 12 months, the tumor-induced state of T-cell-mediated immunosuppression generated in syngeneic mice in response to growth of an immunogenic tumor will be subjected to further analysis. The experimental model to be employed will be the same as that employed previously. It will consist of T-cell deficient, tumor-bearing test recipients, the tumors of which can be caused to completely regress by intravenous infusion of tumor-sensitized T-cells from tumor-immune donors. The splenic T-cells from tumor-bearing donors which can suppress this adoptive T-cell-mediated regression of established tumors will be examined in terms of their: (a) surface Lyt antigens, (b) susceptibility to cytoxic drugs and X-irradiation, (c) kinetics of production in response to tumor growth, (d) functional life-span after tumor excision, (e) capacity to replicate in response to tumor specific antigens and (f) propensity for entering sites of inflammation. In a separate study, the immunotherapeutic action of Corynebacterium parvum will be analyzed in terms of its capacity to potentiate the production of T-cells capable of specifically lysing cells of the syngeneic P-815 mastocytoma. Suppressor T-cells generated in response to growth of this tumor will be tested for that capacity to suppress the immunopotentiating action of C. parvum.